This invention generally relates to engines having crankcases enclosing moving parts lubricated and cooled by lubricating oil. More particularly the invention relates to an engine crankcase in which the cooling performance of the lubricating oil is improved, and at the same time leakage of gear meshing noise to the outside is prevented.
As is known, moving parts requiring lubrication such as meshed gear parts assembled within an engine are so constructed and arranged as to be lubricated and cooled by a lubricating oil which is circulated in the engine, and this lubricating oil absorbs heat from these parts requiring lubrication, whereby its temperature rises.
When the temperature of this lubricating oil rises excessively, the oil viscosity decreases, and the oil-film-forming capability of the lubricating oil drops, whereby not only does it become difficult to obtain good lubrication, but this causes deterioration of the oil.
A number of measures intended to overcome this difficulty have been proposed. For example, Japanese Utility Model Laid-Open Publication No. 46940/1979 discloses a technique which comprises providing baffle plates on the outer side of the crankcase and directing at least a portion of the cooling air draft propelled by the cooling fan to flow down along the outer surface of the crankcase thereby to accomplish cooling of the lubricating oil within the crank chamber through the crankcase.
This technique of the prior art, however, requires the troublesome work of installing the baffle plates and entails an increase in labor cost.
Within an engine crank chamber, in general, a plurality of gears such as cam gears and balancer gears are assembled in meshed state and emit meshing noise as the engine operates. However, with respect to this gear meshing noise, no serious countermeasure has heretofore been taken as far as we are aware.